Self-healing plastic oozes fluids to mimic blood clots

If you prick it, does it not bleed? Puncture this plastic and it will heal itself with oozing fluids, in a process that mimics the way blot clots form to repair wounds. The plastic could one day be used to automatically patch holes in distant spacecraft or repair fighter jets on the fly.

Now his team have created a plastic lined with a type of artificial vascular system that can heal damage large enough to be visible to the naked eye.

The key is a pair of liquids that react when they are mixed. One fluid contains long, thin molecules and the other contains three-sided molecules. When the fluids mix, the molecules join together to create a scaffold, similar to the way blood platelets and fibrin proteins join to form a clot.

After a few minutes of contact, the liquids turn into a thick gel that fills the damaged area. Over a few hours, other ingredients within the fluids cause the gel to harden.

Strength from weakness

To test the concept, the team ran separate channels of each liquid through a plastic square and punctured it, creating a 4-millimetre hole with 35 millimetres of surrounding cracks. This also tore open the fluid channels.

Pumps on the edge of the plastic quare squirted the fluids into the channels, where they oozed out and mixed, filling the hole and the radiating cracks within 20 minutes. The material hardened in about 3 hours, and the resulting patch was around 60 per cent as strong as the original plastic.

Holes larger than 8 millimetres proved more difficult to fill, as gravity caused the gel to sag before it could harden. The team thinks using foams in place of fluids would fill larger gaps, but they haven't tested that idea yet.

Eventually, White and his team envision plastics with multiple criss-crossing channels, to ensure that the fluids always overlap with a damaged area. Embedding this synthetic vascular network would weaken the original material, but not by much, they say.

"You pay the price for being able to repair this damage, but it is certainly one that nature has figured out how to tolerate," says team member Jeff Moore, also at the University of Illinois. "If you just look to things like bone or trees, they are all vascularised."

Remote repairs

The first applications could be in objects in remote locations that are difficult to repair. For instance, self-healing material would be useful on spacecraft, which can become pock-marked by mini meteors, or on drilling equipment at the bottom of deep wells. Self-healing shields for the military are also a likely application – the work was funded by the US air force.

For now, the complexity of creating a full vascular system in a material will limit it to high-end uses where the materials are already robust, says Ibon Odriozola at the CIDETEC Centre for Electrochemical Technologies in San Sebastián, Spain, who previously created a rubbery self-healing material. "For very tough composites, I think this is the best approach," he says.

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